Method of cleaning and bleaching artificial fibers



Patented Feb. 4, 1941 UNITED STATES PATENT OFFICE METHOD OF CLEANING AND BLEACHING ARTIFICIAL FIBERS Helmuth- Korte and Erich Kayser, Frankfort-onthe-Main, and Erich- Schwartz, Mannheim, Germany, assignors to I. G. Farbenindustrie Aktiengesellschaft, Frankfort on the Main,

Germany No Drawing. Application February 11, 1939, Se-

rial No. 255,858. In Germany February 19,

9 Claims.

bath and if necessary in a washing bath the threads are treated in the usual manner with alkaline hypochlorite lye or with a liquidcontaining an oxidising agent, such as a peroxide, in order to improve the degree of whiteness.

As long as linters or the like wereused as cellulosic raw material required for the preparation of the cellulose solution, there was no difiiculty in obtaining purely white artificial threads even when the treatment with alkaline hypochlorite was short. Owing to the increasing application of wood and straw celluloses for the production of the cellulose solutions, the known cleaning andbleaching methods no longer suffice. In spite of a previous cleaning of the cellulose purified and bleached by any method, the cellulose solutions, such as the viscose solutions,

2 nearly always still contain small portions of lignin, hemi-cellulose or the like, which impart to the spun artificial thread a more or less brownish color and are removed by the usual methods only with consumption of much chemical and time; the manufacture of the threads is, of course considerably retarded'because the prolonged bleaching period upsets the continuous spinning operation. Now we have found that this drawback may 35 be avoided by treating with an acid chlorine bath of a pI-I value smaller than 6 and containing at least 0.1 per cent of active chlorine the artificial fibers, for instance bundles of artificial fibers spun from a wood cellulose solution which is prepared from raw materials containing lignin or fibers of this kind cut to staple length, after they have been treated in a coagulation bath or in a washing bath but before any desulfurizing treat- 'ment. It is immaterial whether the acid chlorine bath consists of chlorine water or is produced by acidifying hypochlorite solution. One procedure is as follows: the bundle of fibers which after the coagulation bath has been treated with acid is introduced into a hypochlorite solution without removing the adhering acid. By the quantity of acid introduced together with the bunch of fibers the hypochlorite solution is directly adjusted to the desired pH-value. After a short treatment with the acid chlorine bath the fibrous material is freed from the main portion of liquid containing chlorine, for instance by squeezing, and then treated with an alkaline hypochlorite bath preferably until the reaction between the active chlorine still present and the impurities is complete and 'the fibers have been entirely bleached. Instead of the hypochlorite bath there may be used an alkali bath for -in-- stance a weak caustic soda solution or caustic potash solution or a mixture of both solutions or a bath of another compound of alkaline reaction, for instance sodium carbonate, sodium sulfide, or solutions of borates or of sulfites; a suflicient quantity of hypochlorite is formed by the quantity of chlorine introduced together with the fibrous material, and this is suflicient for the cleaning or bleaching. If, for instance cellulose acetate threads are spun from a cellulose acetate solution, the bath following the acid chlorine treatment, suitably after an intermediate rinsing will consist of chemicals of mild alkaline reaction, in order to prevent a saponification of the acetate groups, for instance a sodium sulfite solution; if necessary a raised temperature may be applied for this treatment.

For various fibrous substances a simple treatment with acid chlorine solutions of a pH-value smaller than 6 is already sufficient; the alkaline after-treatment in this case may be omitted.

The process may also be modified by rinsing the artificial fibers after the acid chlorine treatment and then treating them in a bath containing alkaline oxidizing agents, for instance a peroxide bath, if necessary at a raised temperature.

The following examples serve to illustrate the invention, but they are not intended to limit it thereto:

(1) A cable of artificial cellulose fibers spun according to any desired process from a cellulose solution is, after pressing as usual passed from the precipitating bath without interruption, if desired, whilst supported on a known device, first through an acid chlorine bath containing per liter about 1 gram of active chlorine and about 0.8 gram of hydrochloric acid and, without an intermediate rinsing through an alkaline chlorine bath containing per liter about 2 grams of active chlorine and 0.5 gram of calcined sodium carbonate; the fibers are then rinsed and after-treated as usual.

(2) A cable of artificial cellulose fibers is im-' pregnated after leaving the precipitating bath with acid chlorine baths containing per liter about 2 grams of active chlorine and 1.8 grams of hydrochloric acid; these baths are caused to act upon the material for about 1 minute. The fibers are then passed through a rinsing bath and finally treated in an alkaline bath containing per liter about 1 gram of KOH. Instead of subjecting the material to a treatment with a caustic potash solution, it may be treated with chemicals of a mild alkaline reaction, for instance calcined sodium carbonate or sodium sulfite baths, if required at a raised temperature, for instance 60' C.-80 C.

(3) Freshly spun cellulose staple fibers are treated without interruption first with a sulfuric acid bath containing l-lzsOi of about 5 B. specific gravity, then with an acid chlorine bath containing per liter 1.25 grams of active chlorine and 1.0 gram of hydrochloric acid and finally,

with or without an intermediate rinsing, with an.

oxygen bath containing per liter 0.2 gram of active oxygen and 1.5 grams of sodium pyrophosphate.

We claim:

l. A method of cleaning and bleaching artificial fibers spun from a cellulose solution pre-. pared from cellulose raw materials containing lignin which method comprises treating the artificial fibers after having left the precipitating bathbut before desulfurizing, with at least one acid chlorine bath of a pH-value smaller than 6 containing at lea-st 0.1 per cent of active chlorine together with mineral acids.

2. A method of cleaning and bleaching artificial fibers spun from a cellulose solution prepared from cellulose raw materials containin lignin which method comprises treating the artificial fibers after having left the precipitating bath but before desulfurizing and passingthrough a washing bath, with at least one acid chlorine bath of "a pH-value smaller than 6 containing at least 0.1 per cent of active chlorine together with mineral acids.

3. A method of cleaning and bleaching arti-.

ficial fibers spun from a cellulose solution pre pared from cellulose raw materials containing lignin which method comprises treating the artificial fibers after having left the precipitating bath but before desulfurizing with at least one acid chlorine bath of a pH-value smaller than 6 containing at least 0.1 per cent of active chlorine together with mineral acids, eliminating the main portion of the liquid containing chlorine and causing the excess of active chlorine to react in an alkaline bath with the impurities still present.

4. A method of cleaning and bleaching artificial fibers spun from a cellulose solution prepared from cellulose raw materials containing lignin whichmethod comprises treating the artificial fibers after having left the precipitating bath but before desulfurizing with at least one acid chlorine bath of a pH-value smaller than 6 containing at least 0.1 per cent of active chlorine together with mineral acids, eliminating the main portion of the liquid containingchlorine and causing the excess of active chlorine to react in an alkaline hypochlorite bath with the impurities still presen 5. A method of cleaning andbleaching artificial fibers spun from a cellulcse solution pre,-

pared from cellulose raw materials containin lignin which method comprises treating the artificial fibers after having left the precipitating bath but before desulfurizing with at least one acid chlorine bath of a pH-value smaller than 6 containing at least 0.1 per cent of active chlorine.

together with mineral acids, eliminating by squeezing the main portion of the liquid containing chlorine, subjecting the fibers to an intermediate rinsing and completing the bleaching of the fibers in an alkaline peroxide bath.

6. A method of cleaning and bleaching artificial fibers spun from a cellulose solution prepared from cellulose raw materials containing lignin which method comprises treating the artificial fibers after having left the precipitating bath but before desulfurizing and passing through a washing bath with at least one acid chlorine bath of a pH-value smaller than 6 containing at least 0.1 per cent of active chlorine together with mineral acids. eliminating the main portion of the liquid containing chloof artificial fibers spun from a cellulose solution prepared from cellulose raw materials containing lignin which method comprises removing the main portion of the liquid from the hanks after they have left the precipitating bath but before desulfurizing by pressing them, passing them through an acid chlorine bath containing per liter about 1 gram of active'chlorine and 0.8 gram of hydrochloric acid andwithout an intermediate rinsing through an alkaline chlorine bath containing per liter about ,2 grams of active chlorine and 0.5 gramof calcined sodium carbonate and finally rinsing the hanks and subjecting them to the usual after-treatment.

- 8. A method of cleaning and bleaching hanks of artificial cellulose fibers spun from a cellulose solution prepared from cellulose raw materials containing lignin which method comprises impregnating the hanks before desulfurizing with acid chlorine baths containing about 2 grams of active chlorine and 1.8 grams of hydrochloric acid per liter, causing this liquid to act for about 1 minute upon the hanks, rinsing them and treating them in an alkaline bath containing per liter about 1 gram of potassium lye.

9. A method of cleaning and bleaching staple fibers spun from a cellulose solution prepared from cellulose raw materials containing lignin 

